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Turbulent heat transfer in a horizontal helically coiled tube

Heat Transfer - Asian Research 1999年第5期28卷 395-403页

作者： Bai, Bofeng Guo, Liejin Feng, Ziping Chen, Xuejun State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University China

An experiment has been conducted in detail to study the turbulent heat transfer in horizontal helically coiled tubes over a wide range of experimental parameters. We found that the enhancement of heat transfer in the coils results from the effects of turbulent and secondary flows. With Reynolds number increasing to a high level, the contribution of the secondary flow becomes less to enhance heat transfer, and the average heat transfer coefficient of the coil is closer to that in straight tubes under the same conditions. The local heat transfer coefficients are not evenly distributed along both the tube axis and the periphery on the cross section. The local heat transfer coefficients on the outside are three or four times those on the inside, which is half of the average heat transfer. A correlation is proposed to describe the distribution of the heat transfer coefficients at a cross section. The average cross-section heat transfer coefficients are distributed along the tube axis. The average value at the outlet section should not be taken as the average heat transfer coefficient.

关键词： Heat transfer

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Possible consumption pathways of 2,5-dimethylfuran in low-pressure premixed laminar flames 7

Possible consumption pathways of 2,5-dimethylfuran in low-pr...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Wu, X.S. Wei, L.X. Huang, Z.H. Yuan, T. Zhang, K.W. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei230029 China

Low-pressure (4.0 kPa) premixed laminar 2,5-dimethylfuran (DMF)/oxygen/argon flame with an equivalence ratio (ø) of 2.0 was studied with tunable vacuum ultraviolet synchrotron radiation photoionization and molecular-beam mass spectrometry. Photoionization mass spectrum of DMF/O2/Ar flame was recorded and the photoionization efficiency curves (PIEs) of the combustion intermediates were measured. Flame species, including isomeric intermediates, are identified by comparing the measured ionization energies with those reported in literatures or those calculated with Gaussian-03W procedure. More than 70 species have been detected, including furan and its derivatives, aromatics, free radicals, and so on. Possible reaction pathways of DMF are proposed based on the intermediates identified. DMF can be consumed by H-abstraction and pyrolysis reactions. © 2009 Combustion Institute. All rights reserved.

关键词： Free radicals

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Effects of hydrogen addition on spherically expanding n-butane flames

Effects of hydrogen addition on spherically expanding n-buta...

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Fall Meeting of the Eastern States Section of the Combustion Institute 2009

作者： Tang, Chenglong Li, Yuyang Huang, Zuohua Law, C.K. State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an710049 China Department of Mechanical and Aerospace Engineering Princeton University PrincetonNJ08544 United States

ISBN: (纸本)9781615676682

Laminar flame speeds of hydrogen blended n-butane flames at atmospheric pressure and room temperature was measured in a combustion vessel with Schlieren photography, and determined using nonlinear regression analysis. According to the hydrogen addition parameter (RH) and effective equivalence ratio (φF) defined by Yu et al (1986), laminar flame speeds (Suo) for φF between 0.6 and 1.4 were found to increase linearly with RH from 0 to 0.5, with the slope of the variation assuming a minimum around stoichiometry. These experimental results correlate well with computed laminar flame speeds using the detailed reaction mechanism, USC Mech II. Furthermore, the adiabatic flame temperature was found to also increase monotonously with RH at specific φF, with the extent of the increase being the smallest around stoichiometry. It is therefore suggested that the effect of hydrogen addition on the laminar flame speeds of n-butane flames can be satisfactorily correlated with the response of the corresponding adiabatic flame temperature.

关键词： Stoichiometry

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Thermoelectric characteristics analysis of TOPAZ-II

Thermoelectric characteristics analysis of TOPAZ-II

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2019 Transactions of the American Nuclear Society, ANS 2019

作者： Dai, Zhiwen Wang, Chenglong Liu, Xiao Zhang, Dalin Qiu, Suizheng Su, Guanghui School of Nuclear Science and Technology Shanxi Engineering Research Center of Advanced Nuclear Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

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Optimization of thermal spray parameters of nial/cr2c3 coating by taguchi method

Optimization of thermal spray parameters of nial/cr2c3 coati...

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Asia Conference on Material and Manufacturing Technology, ACMMT 2018

作者： Tahari, M. Luo, B. Geng, J. Jing, D. Hatami, M. EsfarayenNorth Khorasan Iran International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9783035714050

In this study the effect of thermal spray process on wear resistance of NiAl/Cr2C3 thermal spray coating has been investigated. For this purpose the NiAl power mixed with 10 %wt. Cr2C3 powder and milled for 1 hrs at argon atmosphere. The APS parameters such as voltage (V), current(A), spray distance (mm), powder feed rate (gr/min), were optimize using a response surface methodology. For investigation effect of spray parameters on quality of coatings, the porosity and wear resistance of coatings analyzed with SEM and pin on disk wear test. Results show that increase of voltage and current are more effective other parameters. Increasing of powder feed rate and spray distance raised porosity of coatings intensively. © 2019 Trans Tech Publications Ltd, Switzerland.

关键词： Taguchi methods

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Effect of nozzle diameter on spray and thermal characteristics of R134a flashing spray 13

Effect of nozzle diameter on spray and thermal characteristi...

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13th International Conference on Liquid Atomization and Spray Systems, ICLASS 2015

作者： Zhou, Z.F. Wang, R. Chen, B. Wang, G.X. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Department of Mechanical Engineering University of Akron AkronOH44325-3903 United States

Two-phase flashing spray holds a special interest in the safety area. High pressure liquids or liquefied gases accidentally released from small hole in chemical or nuclear industry can form two-phase mixtures due to the rapid decrease of pressure, resulting in injuries, fatalities, serious local pollution, etc. Besides, flashing spray has been successfully used in laser dermatology to prevent thermal injuries during recent decade. In this work, an experimental study is conducted to characterize the two-phase flashing spray in the close field of flashing occurrence and quantify the effect of nozzle diameter on the spray and thermal characteristics, using the volatile and low boiling point cryogen of R134a. From the axial and radial distributions of droplet diameter, velocity and average temperature, it is found that droplet diameter and average temperature experience rapid decline along the axial spray distance, and the velocity has acceleration near the nozzle exit due to the explosive atomization. Droplet diameter keeps almost constant except at the spray periphery, and droplet velocity decreases linearly in the radial direction. Droplet average temperature has complex variation along the radial distance depended on the axial distance. Nozzle diameter has significant effect on the spray and thermal characteristics. Larger diameter nozzle results in longer acceleration distance of droplet velocity, whereas smaller diameter nozzle causes higher decrease rate of droplet diameter and temperature near the nozzle exit. Nevertheless, nozzle diameter has little effect on the minimum droplet temperate with the same value of -60oC. The dimensional analysis indicates that the non-dimensional lateral velocity profile and the non-dimensional droplet average temperature in the spray centerline all show self-similarity. New correlations of non-dimensional droplet velocity and average temperature are proposed. © 2015 International Conference on Liquid Atomization and Spray Systems

关键词： Velocity

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Research on the hydraulic characteristics of a 600MW supercritical pressure CFB boiler

Research on the hydraulic characteristics of a 600MW supercr...

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20th International Conference on Fluidized Bed Combustion

作者： Yang, D. Pan, J. Bi, Q.C. Zhang, Y.J. Jiang, X.G. Yu, L. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Harbin Boiler Co. Ltd. Harbin 150046 China

Water wall design is a key technology of supercritical pressure CFB boiler. On account of the low heat flux and its homogeneous distribution in furnace, internally ribbed tubes with low mass flux and smooth tubes with moderate mass flux can be applied in the water wall of supercritical CFB boilers. An experimental research on the flow and heat transfer characteristics of internally ribbed tubes and smooth tubes with different inner diameters was conducted in the range of sub-critical and supercritical pressure. The departure from nucleate boiling (DNB) and dry-out boundary and the empirical correlations of heat transfer are obtained from the experiments. The mathematical model for predicting the circuit mass flux and grid pressure of a flow network system is based on the mass and momentum conservation equations and an iterative method is used to solve the nonlinear equations. Harbin Boiler Works has developed a 600MW supercritical CFB boiler with external heat exchangers and 6 separators. The mass flux and metal temperature distribution of water wall in the CFB boiler are calculated and the results show that the water wall can operate safely at BMCR and 75%BMCR load.

关键词： Nonlinear equations

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Low pressure premixed laminar n-heptane+propane/oxygen flames studied with tunable synchrotron photoionization 7

Low pressure premixed laminar n-heptane+propane/oxygen flame...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Yu, W. Wei, L.X. Ma, Z.H. Huang, Z.H. Yuan, T. Tian, Z.Y. Li, Y.Y. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei230029 China

Low pressure premixed laminar n-heptane/propane/O2/N2 flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 10%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experimental results provide detailed experimental data in understanding the combustion of n-heptane and n-heptane/propane blends in engine. They are also helpful in establishing and verifying the kinetic model. © 2009 Combustion Institute. All rights reserved.

关键词： Combustion

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flow visualization study of two-phase flashing spray with iso-pentane 14

Flow visualization study of two-phase flashing spray with is...

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14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018

作者： Wang, J.F. Zhou, Z.F. Yang, T. Chen, B. Wang, G.X. Zhao, L. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Department of Mechanical Engineering University of Akron AkronOH44325-3903 United States

The explosive flashing spray commonly occurs during the accidental release of flammable and toxic pressure-liquefied gases in chemical or nuclear industry. This work conducts a small-scale flashing spray experiment in house to simulate the accidental release, aiming to investigate the macroscopic atomization characteristics, which is helpful for the risk assessments and therefore minimizing the impact of the release hazard. The iso-pentane was taken as the working medium, and a transparent straight-tube nozzle with inner diameter of 0.6 mm and length of 40 mm was employed to generate the flashing spray vertically. A high-speed camera was used to record the images of the flashing spray. The whole dynamic evolution was obtained. The effects of injection pressure (0.6 to 2.4 MPa) and initial temperature (40 to 60 oC) were fully explored, respectively. The experiment results indicate that the superheat and injection pressure have a coupled effect on flashing spray. The release of superheat results in phase change with the generation of bubble within liquid, which facilitates the break-up of liquid core and ligament liquid. Meanwhile, the increment of injection pressure can enhance the disturbance of the flow and the number of nucleation. © 2018 Solar Turbines Incorporated.

关键词： Atomization

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Analysis of Frequent Tube Burst of High Temperature Reheater in 600 MW Unit

Analysis of Frequent Tube Burst of High Temperature Reheater...

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2020 IEEE Sustainable power and Energy Conference, iSPEC 2020

作者： Sun, Ke Wang, Jiaan Yan, Yu Jiang, Jiahao Deng, Lei Che, Defu China Huadian Electric Power Research Institute Co. Ltd. Hangzhou310030 China State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'An Jiaotong University Xi'an710049 China

ISBN: (纸本)9781728191645

The reasons of frequent tube burst of the high temperature reheater in a supercritical 600 MW unit were systematically investigated via the examination of macroscopic inspection, chemical composition, mechanical properties, microstructures, scanning electron microscope and energy disperse spectroscopy detection. It is demonstrated that the tube burst of the high temperature reheater results from not only design factors, but also manufacture quality. Due to the absence of solid solution treatment in spare elbow, the inner dislocations and residual stress increase obviously, which accelerates the precipitation of carbide containing Cr and the formation of Cr depleted zone on grain boundary(GB) subsequently, leading to the decrease of GB corrosion resistance and the final leakage of high temperature reheater tube induced by intergranular corrosion. © 2020 IEEE.

关键词： Carbides

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